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The sentinel lymph node (SLN) is the only focus of axillary metastasis in a significant proportion of patients. In this single institutional study, clinicopathologic characteristics were investigated to determine the factors predicting the status of a SLN biopsy and the metastatic involvement of non-SLNs. Data were retrospectively reveiwed for 400 consecutive patients with clinical T1/T2 N0 breast cancer who underwent a SLN biopsy including axillary and/or internal mammary lymph nodes. The SLNs were evaluated by using the new AJCC staging criteria following multiple sectioning and immunohistochemical (IHC) analyses of nodes. The SLN contained metastases in 148 patients (38.5%) including 18 patients (12.2%) with micrometastases (≤0.2mm) and 130 patients (87.8%) with macrometastases (>0.2cm). Five patients had isolated tumor cells detected by IHC (≤0.2mm, N0i). Patients with tumor size more than 2cm (T1, 29.8% versus T2, 51.6%; OR=2.31, 95% CI, 1.50–3.56) and lymphovascular invasion (LVI-, 30.3% versus LVI+, 51.3%; OR=2.07, 95% CI, 1.34–3.19) were more likely to have positive SLNs in both univariate and multivariate analyses. Among patients with a positive SLN biopsy, those with T2 tumors (versus T1; 63.1% versus 36.9; OR=2.93, 95% CI, 1.43–6.04), macrometastases in SLNs (versus micrometastases; 88.9% versus 11.1%; OR=8.83; 95% CI, 1.82–42.87) and extracapsular node extension (versus without extracapsular node extension; 65.4% versus 34.6%; OR, 2.23; 95% CI, 1.05–4.72) were more likely to have non-SLN metastases in both univariate and multivarite analyses. These results indicate that clinicopathologic factors might be helpful to select patients who were less likely to have negative SLN or non-SLNs. However, additional factors are still needed to be identified to omit surgical axillary staging.